Mississippi River Delta
Overview
 
The Mississippi River Delta is the modern
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 area of land (the river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

) built up by alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...

 deposited by the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 as it slows down and enters the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

. The deltaic process has, over the past 5,000 years, caused the coastline of south Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

 to advance gulfward from 15 to 50 miles (24 to 80 km).

It is a biologically significant region, comprising 3 million acres (12,000 km²) of coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

al wetlands and 40% of the salt marsh
Salt marsh
A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh...

 in the contiguous United States.
Discussions
Encyclopedia
The Mississippi River Delta is the modern
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 area of land (the river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

) built up by alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...

 deposited by the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 as it slows down and enters the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

. The deltaic process has, over the past 5,000 years, caused the coastline of south Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

 to advance gulfward from 15 to 50 miles (24 to 80 km).

It is a biologically significant region, comprising 3 million acres (12,000 km²) of coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

al wetlands and 40% of the salt marsh
Salt marsh
A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh...

 in the contiguous United States. It is also a commercially significant region, supporting the economy of New Orleans with significant shipping traffic, providing 16 to 18% of the oil supply in the U.S.
Port Fourchon, Louisiana
Port Fourchon is Louisiana’s southernmost port, located on the southern tip of Lafourche Parish, Louisiana, on the Gulf of Mexico. It is a sea port, with significant petroleum industry traffic from offshore Gulf oil platforms and drilling rigs as well as the Louisiana Offshore Oil Port pipeline...

, and providing 16% of the fisheries harvest in the U.S., including shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s, and crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

.

The Mississippi River Delta is not to be confused with the Mississippi Delta
Mississippi Delta
The Mississippi Delta is the distinctive northwest section of the U.S. state of Mississippi that lies between the Mississippi and Yazoo Rivers. The region has been called "The Most Southern Place on Earth" because of its unique racial, cultural, and economic history...

 region, an alluvial plain
Alluvial plain
An alluvial plain is a relatively flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms...

 located some 300 miles (482.8 km) northward in western Mississippi
Mississippi
Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...

 along the river.

Recent influences

About every thousand years, the Mississippi River has changed course. Each Mississippi River deltaic cycle was initiated by a gradual capture of the Mississippi River by a distributary which offered a shorter and steeper route to the Gulf of Mexico. After abandonment of an older delta lobe, which would cut off the primary supply of fresh water and sediment, an area would undergo compaction, subsidence
Subsidence
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...

, and erosion. The old delta lobe would begin to retreat as the gulf advanced, forming bayou
Bayou
A bayou is an American term for a body of water typically found in flat, low-lying areas, and can refer either to an extremely slow-moving stream or river , or to a marshy lake or wetland. The name "bayou" can also refer to creeks that see level changes due to tides and hold brackish water which...

s, lakes, bays, and sounds
Sound (geography)
In geography a sound or seaway is a large sea or ocean inlet larger than a bay, deeper than a bight and wider than a fjord; or it may be defined as a narrow sea or ocean channel between two bodies of land ....

.
The river has been diverting more of its flow to the Atchafalaya River
Atchafalaya River
The Atchafalaya River is a distributary of the Mississippi River and Red River in south central Louisiana in the United States. It flows south, just west of the Mississippi River....

, which branches off some 60 miles (95 km) northwest of New Orleans. In the mid-20th century, engineers observed that the Mississippi would soon abandon its current channel as the mainstream, and instead migrate to the Atchafalaya Basin
Atchafalaya Basin
The Atchafalaya Basin, or Atchafalaya Swamp, is the largest swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atchafalaya River and the Gulf of Mexico converge. The river stretches from near Simmesport in the north...

.

Because there is extensive economic development along the current path of the Mississippi, and because extensive flooding and evacuation would occur in the new area, Congress instructed the Army Corps of Engineers to maintain the then-present 70% / 30% distribution of water between the Lower Mississippi and the Atchafalaya River channels, respectively. They did so by building the Old River Control Structure
Old River Control Structure
The Old River Control Structure is a floodgate system located in a branch of the Mississippi River in central Louisiana. It regulates the flow of water leaving the Mississippi into the Atchafalaya River, thereby preventing the Mississippi river from changing course. Completed in 1963, the...

, which consisted of massive floodgates that could be opened and closed as needed at the entrance to the Old River.

Manmade changes to other parts of the Mississippi River have had a pronounced effect on the Delta region. Dams, artificial channeling, and land conservation measures have caused a decrease in sediment carried into the delta region, decreasing the rate of build up of the Delta. The currently active lobe is called the Birdfoot (after its shape) or Balize Delta (after the first French settlement La Balize
La Balize, Louisiana
La Balize, Louisiana, was the first French fort and settlement near the mouth of the Mississippi River in what became Plaquemines Parish. The village's name meant "seamark". Inhabited by 1699, La Balize was one of the oldest French settlements within the current boundaries of Louisiana...

 at the mouth of the river). It has been active for 600-800 years.

Extensive oil and gas extraction has also resulted in subsidence of the delta and wetlands causing the loss of 34 square miles (88.1 km²) of land every year. Since 1930, Louisiana has lost 1200000 acres (4,856.2 km²) of coastline.

At the same time, the rate of loss of the Delta has recently increased past the rate of build up, causing a net loss of wetlands in the Delta area. The rise in sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 has caused increased erosion, as the fresh water vegetation that previously protected against erosion dies due to the influx of salt water. Subsidence
Subsidence
Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...

 has increased.

History


Build-up of the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

 shoreline due to the outflow of the Mississippi River has been occurring in a periodic fashion since the late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 period. This same process is responsible for build up of the larger Mississippi embayment
Mississippi embayment
The Mississippi Embayment is a physiographic feature in the south-central United States, part of the Mississippi Alluvial Plain. It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois. The embayment...

; however, the delta region is the most recent and ecologically
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 distinct portion.

The latest cycle of delta movement can be traced to the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

 epoch, when a large amount of ocean water was tied up in glaciers. The sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 was 300-400 feet (~100m) below present level, and causing the mouth of the Mississippi to be located further out into the Gulf of Mexico. 10,000 years ago, the glaciers began to melt, and the sea level began to rise. 5,000 - 6,000 years ago, the sea level stabilized, and formation of recognizable modern deltas began.

Lake Pontchartrain
Lake Pontchartrain
Lake Pontchartrain is a brackish estuary located in southeastern Louisiana. It is the second-largest inland saltwater body of water in the United States, after the Great Salt Lake in Utah, and the largest lake in Louisiana. As an estuary, Pontchartrain is not a true lake.It covers an area of with...

 was formed during the evolution of two separate delta lobes. 4000-3800 years ago, the Cocodrie lobe * expanded over the area where New Orleans presently resides, forming the lake's southern shore. 2800-2600 years ago, the St. Bernard lobe * pushed forward and completed the lake's eastern shoreline. Lafourche delta lobe (shown in blue) was the youngest abandoned lobe. It reached just south of where Venice is today. The active Birdfoot or Balize delta lobe is shown in cream on the image.

In 1699 the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 built their first crude fort at La Balize, on the Southeast Pass in Pass á Loutre, to control passage on the Mississippi. By 1721 they had built the wooden lighthouse-type structure (la balise means seamark in French) that gave the settlement its name. Built in the marshes, the village was vulnerable to hurricane damage. In addition, ships had to deal with the shifting conditions of tides, currents and mudflats through the mouth of the delta. From 1700 to 1888, the main shipping channel was changed four times in response to shifting sandbars, mudflats and hurricanes. La Balize was moved by 1853 to the Southwest Pass
Southwest Pass (Mississippi River)
Southwest Pass is one of the channels at the mouth of the Mississippi River. It empties into the Gulf of Mexico at the southwesternmost tip of the Mississippi River Delta. It lies in Plaquemines Parish in southeastern Louisiana in the United States...

 when that became the main shipping channel, then rebuilt at Pilottown about five miles (8 km) upriver above Head of Passes
Head of Passes
Head of Passes is where the main stem of the Mississippi River branches off into three distinct directions at its mouth in the Gulf of Mexico: Southwest Pass , Pass A Loutre and South Pass...

 after being destroyed by a hurricane. The Southwest Pass is currently the main shipping channel, with secondary uses at the South Pass and Pass á Loutre.

See also

  • Mississippi Valley Division
    Mississippi Valley Division
    The United States Army Corps of Engineers Mississippi Valley Division and the complementary Mississippi River Commission are responsible for maintaining the Mississippi River as a navigable waterway while preventing flooding. This includes the operation of harbor and lock and dam facilities up...

     of the United States Army Corps of Engineers
    United States Army Corps of Engineers
    The United States Army Corps of Engineers is a federal agency and a major Army command made up of some 38,000 civilian and military personnel, making it the world's largest public engineering, design and construction management agency...

  • Mississippi embayment
    Mississippi embayment
    The Mississippi Embayment is a physiographic feature in the south-central United States, part of the Mississippi Alluvial Plain. It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois. The embayment...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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